Abstract: Abstract: To study the nitrogen retention efficiency of riparian vegetation buffers of small and medium-sized rivers, the common broad-leaved species in Northeast China were slected on the slope of Hejiagou, Harbin in Northeast China. Four riparian planted woodlots of 15 m long by 30 m wide were prepared for the different species experiment, namely bare ground, water willow or ash, five-leaf maple, and poplar riparian vegetation buffers. The bare ground riparian buffers served as controls. The effects of different riparian buffer widths (0, 5, 10, 20, and 30 m) and different plant species above on nitrogen retention in subsurface runoff at 20 and 40 cm depth were analyzed under the condition of riparian slope (3%) and tree density (540 trees/hm2). At the test sites, PVC pipes with a diameter of 10 cm and a 4-mm partial subsurface runoff intake hole on the left side were used to collect subsurface runoff at soil depths of 20 cm and 40 cm. The PVC pipes were buried when the trees were planted. At the four riparian buffer plots from 0 to 0.5 m, the compound fertilizer was evenly applied using a small fertilizer spreader to simulate nitrogen loss conditions. The fertilizer was applied before rainfall, and the ratio of flow-producing compound fertilizer collected after rainfall was 24:6:35 for nitrogen: phosphorus: potassium, with fertilizer application rate of 61 kg/hm2. When sampling, the upper clear liquid in the tube was pumped out with a small pump, and then all the turbid liquid in the tube was pumped out and drained at the far end of the test site to avoid affecting the experimental results, the clear liquid was sampled into 300 mL plastic bottles and stored in a -4-0 ℃ refrigerator for determination of the nitrogen content of the water samples. The ammonium nitrogen in the runoff was determined spectrophotometrically by the nano reagent, the nitrate nitrogen was determined by a UV spectrophotometry, and the total nitrogen was determined by a UV spectrophotometry using the alkaline potassium persulfate elimination method. The statistical analysis results showed that the depth of subsurface runoff did not significantly interact with riparian buffer width and vegetation type. Therefore, the nitrogen values at 20 and 40 cm soil depth were averaged for the followed analysis on the effects of different widths, different vegetation types and different widths × different vegetation types on nitrogen retention. The results showed that the concentrations of runoff ammonium and nitrate nitrogen gradually decreased in riparian vegetation buffers of 0, 5, 10, and 20 m in width. Thus, the riparian vegetation buffer with a width of 20 m could retain all forms of nitrogen well. The 30 m width riparian vegetation buffer had the highest retention of ammonium nitrogen, nitrate nitrogen, and total nitrogen in runoff with 70.4%, 67.7%, and 69.1%, respectively. in the comparison of different plant species buffer zones, poplar could significantly reduce the runoff ammonium nitrogen and total nitrogen concentrations, and water willow could significantly reduce the runoff, the poplar significantly reduced runoff ammonium and total nitrogen concentrations, and ash significantly reduced runoff nitrate-nitrogen concentrations. In the interaction between width and plant species, poplar buffer strips of 20 m width had the highest retention rate of ammonium nitrogen and nitrate nitrogen, and the poplar buffer strips of 30 m width had the highest retention rate of 62.1% for total nitrogen. The results of the study can provide valuable information for the design of riparian buffers to maximize the retention of runoff nitrogen pollutants in small and medium-sized rivers in Northeast China.